1. Field of the Invention
The present invention relates to the field of oil and/or gas well casing perforation apparatus, procedures and methods. More specifically, the invention relates to a unique apparatus and method employing a hydraulic motor driven mill bit for cutting an opening in a well casing to permit the subsequent cutting of a passageway through the surrounding earth by the use of a high pressure jet lance movable through the opening for a substantial distance outwardly beyond the casing for permitting the flow of liquid or gaseous hydrocarbons into the casing.
A contaminated zone is typically formed around the well bore as a result of drilling fluids used during the drilling operation, and also as a result of the cement which is typically forced down into the bottom of a well bore and up into the annular cavity between the well casing the completed well bore. This contaminated zone frequently presents a substantial barrier to the inflow of hydrocarbons to the well casing.
A number of expedients have been proposed and employed in an effort to provide flow passageways through the surrounding strata for permitting and increasing the flow of hydrocarbons into the well casing.
U.S. Pat. Nos. 4,790,384 and 5,107,943 show a method employing a cam drive cylinder means for driving a wedging cam to extend a radially movable punch outwardly through the casing of a well. Another common expedient for effecting casing and formation penetration is the use of projectiles fired from gun-like devices positioned in the casing.
Other U.S. patents have shown separate mechanical cutting devices that are lowered to the bottom of the well, operated to cut a hole through the well casing and subsequently removed from the well casing in order to permit the lowering and positioning of a jet means in the casing for subsequent usage of the nozzle jet-type cutter to cut into the surrounding formation. The positioning and removal of tools such as cutting devices to and from the well normally requires a time consuming and expensive pulling and replacement of the pipe string extending above the tooling. With this method it is also difficult to precisely locate the opening created by the mechanical cutting device at a deep well depth after the cutting device has been removed from the well. The foregoing problem is of substantial significance since the jet-type cutter must be accurately positioned adjacent the opening in order to function.
In the previous patents disclosing a radially movable punch for penetrating through the well casing, the nozzle extension device or lance which moved axially outwardly through an axial bore in the punch and therefore radially relative to the well casing, was forced to make a sharp 90.degree. turn in order to exit from the axial bore through the punch. The resulting small bend radius for the lance necessitated a relatively flexible lance having a relatively small inner diameter. As a result, an undesirable pressure drop occurred through the lance. Furthermore, the wedging mechanism required in these previous patents was very heavy and expensive to build. Another inherent disadvantage of some of the prior art devices is a result of the reaction force created on the punch of the type shown in U.S. Pat. No. 5,107,943 during the penetration of the well casing. This reaction force is of sufficient magnitude to require a back up plate as a part of the down hole apparatus which fits closely to the inner diameter of the well casing. This requirement for a close fit between the down hole apparatus and the well casing can interfere with the ability to locate the down hole apparatus at the proper depth if the well casing has any inside diameter restrictions. Another inherent disadvantage of the methods shown in previous U.S. patents is a lack of reliable means for monitoring the progress of drilling or punching operations being performed at the base of a well bore.